Earlier work has demonstrated that PDTC interferes with the up-regulation of proinflammatory genes by inhibiting the activation of the redox-sensitive transcription factor NF-kappaB. However, other potential mechanisms may also contribute to the widely reported beneficial effects of PDTC. Indeed, we have showed that PDTC attenuates IL-6-mediated activation of the transcription factor STAT3 and expression of acute-phase plasma proteins in hepatocytes. We also reported that STAT3 is susceptible to S-glutathionylation after cell treatment with PDTC, preventing its phosphorylation, dimerization and binding to DNA. Here we report that PDTC induced the release of monomeric HSF1 from the molecular chaperone Hsp90&#945;, with concomitant increase in HSF1 trimer formation, translocation to the nucleus, and binding to promoter of target genes in human HepG2 hepatocarcinoma cells. siRNA-mediated silencing of HSF1 blocked BAG3 gene expression by PDTC. The protein levels of the co-chaperone BAG3 and its interaction partner Hsp72 were stimulated by PDTC in a dose-dependent fashion, peaking at 6 hours. Inhibition of Hsp90 function by geldanamycin derivatives and novobiocin elicited a pattern of HSF1 activation and BAG3 expression that was similar to PDTC. Chromatin immunoprecipitation studies showed that PDTC and the inhibitor geldanamycin enhanced the binding of HSF1 to the promoter of several target genes, including BAG3, HSPA1A, HSPA1B, FKBP4, STIP1, and UBB. Cell treatment with PDTC increased significantly the level of Hsp90alpha thiol oxidation, a posttranslational modification known to inhibit its chaperone function. The results unravel a previously unrecognized mechanism by which PDTC and related compounds could confer cellular protection against inflammation through HSF1-induced expression of heat shock response genes. The main function of heat shock proteins is to prevent accumulation of denatured and/or aggregated proteins that could lead to senescence, neurodegenerative disorders, and cell death. Noteworthingly, HSF1 controls longevity through a stress response-mediated mechanism. Our experiments indicate a novel pathway for HSF1 regulation that could potentially lead to new ways of fighting chronic inflammatory or proliferation-related diseases and increasing longevity.